1. Field of the Invention
The present invention relates to an exhaust control device for a vehicle engine, in which an exhaust valve capable of opening and closing an exhaust valve port provided in a cylinder head to face a combustion chamber is provided in the cylinder head so as to be able to be operatively opened and closed and an exhaust control valve capable of changing the opening area of an exhaust passage is disposed in exhaust passage forming means forming the exhaust passage that has a bent portion and is continuous with the exhaust valve port.
2. Description of Background Art
Japanese Patent Laid-Open No. Hei 2-049936 discloses an exhaust control device for a vehicle engine in which an exhaust control valve, a butterfly valve, is disposed at the bent portion of an exhaust passage that has a bent portion and is continuous with an exhaust valve port.
In the exhaust control device disclosed in Japanese Patent Laid-Open No. Hei 2-049936, a butterfly valve is disposed at the general center of the bent portion in the exhaust passage. When a butterfly valve is fully closed, exhaust passes through between the inner wall of the exhaust passage and the butterfly valve not only at a bent-external portion where a flow rate is high but also at a bent-internal portion where the flow rate is low. Thus, because of the nonconstant exhaust flow rate, it is difficult to control the exhaust flow rate and flow with accuracy.